Production of zwitterion of detergent amino acids



PRODUCTION OF ZWITTERION OFsDETERGENT .AMINO ACIDS ...DonaldtLitAndersen,.Minneapolis, Minn., assignorto "General'Mills,"Inc., a corporation of Delaware No Drawing. .-Applicaflon-August 11, 1955 Serial No." 527,861

6 Claims. (Cl. 260-534) The present invention relates to the production of the zwitteriotljfromi the: salts 10f." ceirtaint detergent: amino acids apresent invention -isdirected are those having*=the-.-foli lowing formula:

"-in*which R- is an aliphatic" hydrocarbon;group-containing from 8-22 carbon atoms and is de'rivdfronradetergent forming fatty acid, R is H or CH Me is alkali metal, m is or 1, n is 1 or 2 but 1 when R is CH;, and the sum of m and n is 2.

Detergent materials of the above formula are frequently made in the form of the sodium or potassium salts and are frequently the hydrolysis products of the corresponding esters or nitriles. The sodium salt of compounds of this type is generally quite alkaline in reaction. For example, sodium dodecylaminopropionate in a 10% aqueous solution has a pH in excess of 12. This is too alkaline for uses in which the material comes in contact with human skin as, for example, in the case of shampoos. Neutralization with mineral acid to an accept able pH level produces considerable inorganic salt. This inorganic salt frequently cannot be tolerated because of solubility and viscosity considerations.

For these reasons it is frequently desirable to convert the sodium or potassium salt to some other more desir able salt and for this purpose the free acid form of the compound is a desirable starting material.

When an excess of mineral acid is added to solutions of the sodium salts of the above detergent amino acids, the zwitterion can be precipitated but in a semi-solid form which is extremely difficult to handle and to purify. Considerable inorganic salt and mineral acid are occluded within the semi-solid mass. The zwitterion thus produced is difiicult to obtain in a salt-free form because the physical form makes washing very tedious.

It has now been discovered that the zwitterion of the detergent amino acids can readily be obtained and purified by a unique procedure.

It is, therefore, an object of the present invention to provide a novel process of producing the zwitterion of the above detergent amino acids and of purifying the zwitterion by a simple series of operations.

It has been discovered that by a careful neutralization of a 10-30% aqueous solution of an alkali metal salt of a detergent amino acid of the above type, by means of sulfuric acid to a pH within the range of 3.5 to 5.5, there results a rapid and complete separation of the reaction mixture into 2 phases. The upper phase comprises a 20-50% aqueous solution containing virtually all of the detergent material contaminated to a slight degree with sodium sulfate dissolved in the solution. This phase is a slightly viscous, clear and readily handled solution. The lower aqueous phase is a solution of sodium sulfate containing only a trace of the de- United States PateiitffO 2,816,920 PatentedDec. 17, 1957 tergent amino acid. The separation is rapid and com- "plete withsno emulsionrproblemsand yieldstapproximately 'sionetparta'of organic phase td';2+3:-:parts sofaaqueousji phase.

This organic phase may be iused'trlirectly ifondhe: production of other salts of the amino acid where a slight amount of sodium sulfate ormther inorganic saltmay be tolerated. It is preferred, however,.to isolate thezwit- ".terion in.si1bstatitially; purejorm. ffThis mayreadily be accomplishedipyf addingthe organic phase slowly. to: a quantity of water 'ab'out2'3"times"that of the organic phase, while.;thewater is being well agitated. "The zwit- .teriori .i s ;.precipitated.as. alinely 'dividedfflocculent semisolid. "The particles 'bf'Tthis' floccillent 'clispersion" remain suspended 'asll'orig as a'gitation' is continued. .When jagiytaltionli is discontinued, the; particles float; to "the. surface "asia fairly compact mass. LTheexcess water may. bedecant'd..afid.the compact, mass may'j be mesu'spefiddQ-in a dde'd wash water. byjsimple agitation. Washing and sfdecaritingmayibe repe'atedanynumber bf times toyield .a;pro"duct which is s'ubstaritiallylfree. fromlinorgahic s'alts, Without. any (significant loss. or. the. zwitterion. '-A .total of 3,. such twa'shings isusually .sjfifiicien't .to.-leech,.out.-i1irtually all oflthe inorganic-salt. "Upon. completion ofjthe washing; the zwitterion maybelseparated.by'idecantation after which residual amounts "of" free water may' be removed by kneading or pressing. As an alternative, the residual water may be removed by melting the zwitterion and then decanting any free water. The resultant prodnot in either event is a gelatinous solid containing approximately 35% water, and is insoluble in water but soluble in alkaline materials.

While sulfuric acid is the preferred acid in that it is less expensive, less corrosive, and requires less accurate control, other known non-oxidizing mineral acids such as hydrochloric and phosphoric may also be used with essentially the same results.

Example 1 A solution of 20.9 lbs. of sodium p-dodecylaminopropionate in 88 lbs. of water was prepared in .a 20 gallon autoclave equipped with an anchor stirrer. To this solution was added slowly and with agitation a solution of 5.2 lbs. of concentrated sulfuric acid in 15 lbs. of water to yield a mixture having a pH of approximately 4.0. Phase separation occurred almost immediately and, upon discontinuing the agitation, the organic phase floated to the top of the aqueous phase and the latter was separated by decantation, sampled for analysis and discarded. The upper organic phase weighed 50 lbs. and was Washed by pouring it in the form of a thin stream into 15 gallons of water under agitation. The organic phase was again permitted to float .and was separated by decantation. The organic phase was subjected to 2 additional washings with 10 gallons of water each. The wash waters were sampled for analysis and then discarded. The final product was approximately solids and had an ash content of less than 0.5%. The following table gives the analyses of the original aqueous phase and the various wash waters.

Solution Percent Percent Percent loss solids ash organic Example 2 The process of Example 1 was repeated with fl,fi'-dodecylaminobispropionate. The zwitterion was obtained in essen y t e S as reported in Example '1.

r -"x A H. A

field and purity tor the zwitterion reported in Example 1,

1 process of Example 1' was repeated: on

dodecylaminocrotonate with essentially the same results Example I The process of Example'l'was carried out substituting .an equivalent quantity of hydrochlaric acid for the sulacid. The results obtained were'essentiallythe same.

I claim as my invention:

1.'Process of prep'armg a zwitterion of acornpound "having the formula RNHMCHRCHfiOOMeL, in

' which R is an' aliphatichydrocarbon group containing from 8- 22'carbon atoms,' R' is selected from the group consisting of hydrogen and'methyl, m is not greater than .1 audit is at least 1 and not more than Z'but is 1 when R is CH and the sum of m and his equal to 2 and Me is alkali metal which comprises" adding a] nonoxidizing mineral acid to an aqueous solution of said alkali metal salt to produce a pH within the rangejof'3.5 to' 5.5 while agitating the solution, discontinuing theagitation to per- 25 mit the precipitated zwitterion thus formed to separate as an aqueous solution in the form of'a' distinct phase and separating the zwi-tterion phase.

2. A process according to claim lin which the mineral acid is sulfuric acid.

3. A process according to claim 1 in which the separated zwitterion is further purified by dispersing the zwitterion 5 in water with agitation, discontinuing the agitation and 2,605,284 Hess July 29, 1952 2,617,823 Wolff et a1 Nov. 11, 1952 2,683,739 Weidman July 13, 1954 OTHER REFERENCES Degering, An Outline of Organic Nitrogen Compounds (1945), page 23 1. i 

1. PROCESS OF PREPARING A ZWITTERION OF A COMPOUND HAVING THE FORMULA RNHM(CHRCH2COOME)N IN WHICH R IS AN ALIPHATIC HYDROCARBON GROUP CONTAINING FROM 8-22 CARBON ATOMS, R'' IS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN AND METHYL M IS NOT GREATER THAN 1 AND N IS AT LEAST 1 AND NOT MORE THAN 2 BUT IS 1 WHEN R'' IS CH3 AND THE SUM OF M AND N IS EQUAL TO 2 AND ME IS ALKALI METAL WHICH COMPRISES ADDING A NONOXIDIZING MINERAL ACID TO AN AQUEOUS SOLUTION OF SAID ALKALI METAL SALT TO PRODUCE A PH WITHIN THE RANGE OF 3.5 TO 5.5 WHILE AGITATING THE SOLUTION, DISCONTINUING THE AGITATION TO PERMIT THE PRECIPITATED ZWITTERION THUS FORMED TO SEPARATE AS AN AQUEOUS SOLUTION IN THE FORM OF A DISTINCT PHASE AND SEPARATING THE ZWITTERION PHASE. 